The purpose of this project is to define the mechanism of regulation of the individual globin genes during erythroid differentiation. Double stranded synthetic copies of the sheep beta B, beta C, and gamma globin genes have been prepared and inserted into the bacterial plasmid, pMB9. A detailed restriction endonuclease map has been derived by analysis of these recombinant plasmids and the synthetic globin genes. A technique has been devised to prepare a single stranded radioactive DNA fragment complementary to the various mRNA species from these recombinant plasmids for use as a hybridization probe. The transcription of the individual globin genes is being studied using the totally pure probes for the individual globin mRNA provided by the recombinant plasmids.